Agarikon Identification Guide

First Impression and Setting

Agarikon is not a mushroom you stumble over. It is a mushroom you spot by looking up. The typical find is a pale, chalky, column-shaped mass hanging off the trunk of a very old conifer, often three to twenty metres above the ground, sometimes higher. From a distance it can read as a bleached wasp nest, a lump of snow that failed to melt, or a beehive fixed to the bark.

The setting narrows things immediately. Laricifomes officinalis is a fungus of structurally old forest. In western North America it grows on western larch, Douglas-fir, and occasionally on hemlocks, true firs and spruces, from British Columbia south through the interior mountains into California. In Eurasia it is a larch specialist, recorded from alpine and Siberian larch stands. It shows a strong preference for large-diameter, old, often damaged trees — living veterans with broken tops, standing snags, and long-dead spars. If you are in a young, even-aged plantation, you are in the wrong forest.

Reading the Fruitbody

Once you have one in hand or in binoculars, work through the shape first. Young conks are roughly hoof-shaped or shelf-like. With age they elongate downward into thick columns, barrel or beehive forms, commonly 10 to 30 cm tall and sometimes reaching 60 cm or more; exceptional specimens are far larger. They are perennial, adding a new growth layer each year, so an old one is a stack of seasons.

The upper surface is white to cream when young, ageing to yellowish, buff or greyish. As it ages it develops concentric zones and horizontal ridges, then cracks into a chalky, crumbling, weathered crust, frequently greened by algae and lichens. The growing edge, when active, is a soft blunt white margin.

The Pore Surface

The underside carries the spore-bearing layer: pores, not gills or teeth. It is white to cream, sometimes discolouring buff where touched or weathered. Pores are small and round, roughly three to five per millimetre — fine enough that from a metre away the surface looks smooth and needs a hand lens to resolve.

Because the fruitbody is perennial, a vertical cut through the underside shows stratified tube layers, each one a season of growth, sometimes separated by thin bands of context tissue. On a hanging column the tubes are always oriented so the pores point straight down, which means that as the conk elongates the tube layers curve to stay vertical. That geotropic correction is worth noticing; it is one of the reasons old specimens have such odd, drooping architecture.

Flesh, Texture and the Chalk Test

The context is the diagnostic tissue here. Break a corner off, or press a fingernail into a fresh margin. In Agarikon the flesh is pure white, soft, and remarkably friable — it crumbles into powder like blackboard chalk and will whiten your fingers. Older, weathered portions become drier and more granular still, but the chalky, non-woody character persists.

This is the fastest way to separate it in the field from almost every other large conk on conifers, since the common bracket fungi of the same forests have tough, corky, fibrous or woody flesh that resists a fingernail. There is no colour change on cutting or bruising beyond a faint buff discolouration.

Taking a Spore Print

Polypores are less obliging than gilled fungi, but a print is possible. Cut a fresh, actively growing piece of the margin, keeping the pore surface intact, and rest it pore-side down on a glass slide or black paper inside a covered container with a damp paper towel to hold humidity. Leave it overnight at room temperature. Fresh material in the growing season deposits a thin white bloom.

Under a microscope, the spores are colourless, smooth, broadly ellipsoid and small, roughly 4 to 5 by 3 to 4 micrometres. A white print is expected and is mainly useful for excluding the brown-spored crust polypores that occupy similar trunks.

Substrate, Season and Ecological Role

Agarikon is a heart-rot fungus. Spores enter through wounds, broken tops and branch stubs, and the mycelium colonises the heartwood of the living trunk, producing a brown cubical rot: decayed wood breaks into rectangular blocks along shrinkage cracks and crumbles between the fingers. The tree can stand and grow for decades while hollowing from the inside, which is exactly why the fungus is tied to veteran trees and why it is uncommon in managed stands.

Because the fruitbodies are perennial they can be found in any month, and a conk may persist for years or decades. Fresh growth, with the soft white margin and a productive pore layer, is added in the growing season. The species is now treated as rare or threatened through much of its range and is used as an indicator of old-growth continuity.

Separating It From Look-Alikes

Fomitopsis pinicola, the red-belted conk, is the usual confusion on conifer trunks. It is hoof-shaped rather than columnar, and its upper surface has a hard, smooth, resinous crust with a distinct orange to red band behind a cream-white margin. Its context is tough, pale and corky, not chalky, and a fingernail leaves a dent rather than powder.

Fomes fomentarius forms grey, hard, strongly zoned hooves, but grows on hardwoods, especially birch and beech, and its brown fibrous context and felty core are nothing like white chalk.

Echinodontium tinctorium occupies similar veteran conifers in the interior west and is also hoof-shaped and cracked, but its underside carries coarse spines and teeth instead of pores, and cutting it reveals a striking brick-red to rusty interior.

Porodaedalea and Phellinus species on pine and fir have brown, woody context, brown pores, and a hard black crust in old age; a drop of alkali turns their flesh dark, whereas Agarikon context stays pale.

Laetiporus brackets are bright orange and yellow, annual, soft and shelving in overlapping tiers, and collapse within weeks.

Fomitopsis rosea is smaller with a pink-tinged pore surface, and Climacocystis borealis is annual, soft, watery-white and hairy, drying hard and shrunken, with much larger irregular pores.

Field Checklist

Look for a big, pale, hoof-to-column-shaped perennial conk high on an old larch or Douglas-fir; a cracked, zoned, chalky-white upper surface; fine white pores in stratified layers; and above all a context that crumbles like chalk under a fingernail. Add brown cubical heartwood rot and an old-growth setting and the identification is secure.